نشریه مهندسی مکانیک مدرس
سال یازدهم شماره 4 (زمستان 1390)

In this study, the potential of controlling engine cooling temperature has been investigated experimentally to reduce NOx emissions in heavy diesel engines. Experiments have been done on 90°C and 70°C cooling temperatures that lower temperature obtained via larger radiator and setting its thermostatic valve. Also, the effects of injection timing and the percentage cooled EGR simultaneously have been studied in order to trade-off NOx reduction and increasing other pollutants such as Soot, CO, HC and fuel economy. Experimental results which related to amount of pollutants and fuel consumption by altering the engine cooling temperature, injection timing, and the percentage of cold EGR shows that NOx emissions reduce 17% averagely also fuel consumption decreases negligible.

In this research work, a comprehensive combustion analysis has been conducted to evaluate the performance of a low speed diesel engine (M8/1 Lister) using biodiesel fuel. Waste vegetable cooking oil as an alternative fuel. Biodiesel obtained from waste vegetable cooking oil (WCO) as an alternative fuel. The properties of biodiesel produced from WCO was measured based on ASTM standards. In order to compare brake power, torques, brake specific fuel consumption (BSFC) and concentration of the UHC and CO emissions of the engine, it has been tested under same load of Dynamometer(5 levels) and biodiesel fuel blends (levels)) at constant engine speed(750 rpm). The results were found to be very comparable. An artificial neural network (ANN) was developed based on the collected data of this work. Multi layer perceptron network (MLP) was used for nonlinear mapping between the input and the output parameters. Different activation functions and several rules were used to assess the percentage error between the desired and the predicted values. The results showed that the training algorithm of Back Propagation was sufficient in predicting the engine torque, brake power, specific fuel consumption and exhaust gas components for different engine loads and different fuel blends ratios.

In this paper, an analytical solution of transient heat conduction in multi-layer composite pin fins under the general boundary conditions is presented. The 2D unsteady heat conduction equation in cylindrical coordinate system has been achieved for multi-layer orthotropic laminates. Laplace transformation is applied to change the solution’s domain from time into the frequency. An appropriate Fourier transformation has been derived using the Strum-Liouville theorem and a set of equations are obtained based on the boundary conditions of fin and temperature/heat flux continuity at boundaries located between the layers. The Meromorphic function method is utilized to find the complicated complex integration of inverse Laplace. Diagrams of unsteady temperature distribution and cooling rate of pin fin have been depicted and it is shown that the effects of orthotropic conduction are more noticeable in high convection coefficients.

In this paper, with the assumption of constant material properties, the nonlinear behavior of beams is studied using the finite element method. To this end, two approaches are represented: in the first approach, the beam is modeled by one dimensional elements of second order that is formulated according to continuum mechanics relationships based on the Lagrangian strategy, while in the second approach based on the Eulerian strategy the nonlinear behavior of the beam is investigated by making use of two dimensional elements. In both approaches, the second configuration, strains and stresses in the beam are obtained via the calculation of deformation gradient.

In the current study fume extraction systems are studied numerically and the effect of various parameters as fresh air inlet gap size, fume temperature and composition as well as the dust size is investigated. To aim this goal a precise 3D model of the entire system and proper grid is generated and system of governing equations for the reactive turbulent two-phase flow is solved using a Finite-Volume based code. The results confirm that although increasing the gap size may lead to a reduction in CO volume fraction, but an increase in products temperature is inevitable. Besides, it is shown that, despite the high efficiency of settling chamber in removing the large size particles (greater than 45 micron), it has a poor efficiency in eliminating the smaller size dust particles.

Contact interfaces are known as the main source of energy dissipation in the structural joints. Therefore it is important in structural dynamic analysis to use predictive joint models which are capable to simulate the structural response and energy dissipation with an acceptable accuracy. In this paper an analytical model is proposed for energy dissipation evaluation due to micro slip mechanism in a beam structure with frictional-free boundary condition. The bending response governing equations are derived under harmonic external excitation and are solved in order to detect transition from stick to slip at the contact interface. The resultant hysteresis loops are obtained and parametric study is done for a numerical case study.

in this paper natural frequencies of a rectangular mindlin plate with surface bounded piezoelectric patches is obtained. Simply supported boundary condition is imposed at the plate edges. Ritz approach based on the principle of minimum potential energy is applied to obtain the frequency parameters of rectangular plate. Since displacement fields of the plate are postulated by trigonometric series function, solution is a semi analytical one. For verifying the accuracy of this method, results are for the isothropic and piezoelectric plates are compared with those reported in the literature. As we see a good conformance is derived from the obtained results and the exact solution. At the end, natural frequencies of a rectangular mindlin with surface bounded piezoelectric patches is obtained.

Possibilities and limitations of 1D and 3D flow simulations in the vaneless turbocharger turbine of a 1.7 liter SI engine are presented experimentally and numerically. A test setup of the turbocharged engine on dynamometer is prepared to validate the results of numerical modeling. Various performance parameters are measured at 12 different engine speeds and the results of measurement in 3 different engine speeds are presented in this report. The complete form of the volute and rotor vanes is modeled. An extensive study on the number of meshes has been undertaken to ensure the independency to meshes. The modeling of rotating wheel is considered by Multiple Rotating Frames (MRF) technique. Finally, the variations of turbine performance parameters are studied under different pulse frequencies of the engine. The results show that at high engine speeds a 3D unsteady flow simulation is required to get reasonably accurate results. The results presented in current report will be used in simulating three dimensional steady and unsteady compressible flow within the turbine of the turbocharger.